Q & A; Spreading Smallpox

By C. CLAIBORNE RAY

Published: March 13, 2007

Q. Would it really have been possible for Europeans to infect Native Americans with the smallpox virus by giving them blankets used by other victims? How long could the virus live on a blanket?

A. It would be at least theoretically possible, experts at the Centers for Disease Control and Prevention said, though some historians doubt that the plan to infect enemy tribes, which the British general Lord Jeffery Amherst notoriously wrote about in 1763, during the French and Indian War, was actually carried out.

Dr. Inger Damon, a researcher and epidemiologist at the centers, said the virus, called variola, lives longer in smallpox scabs than in the droplets spread from person to person, the normal mode of transmission.

''In a humidity-controlled environment, like a cool, dry cabinet,'' Dr. Damon said, ''viruses in scabs have been shown in certain studies to be quite long-lived, from some months to a year, possibly longer.''

Though person-to-person transmission usually requires close, prolonged contact (a distance of about six or seven feet for about three hours), there are reported instances of fabric-borne infections among people who worked in smallpox hospitals, doing laundry or changing bed linens. Even a mortuary worker was infected this way, Dr. Damon said.

''The disease is now eradicated, though the virus lives in a freezer,'' she said, where it is potentially useful for studying the effectiveness of new drugs or vaccines. C. CLAIBORNE RAY